The age-associated loss of skeletal muscle mass and function (sarcopenia) is associated with substantial social and economic costs. The plasticity and adaptability of skeletal muscle to contraction (i.e. resistance-exercise) is a fundamental physiological event leading to larger and more robust skeletal muscle. However, muscle growth in response to resistance exercise (RE), like other anabolic stimuli, is attenuated in older adults The cause of aberrant muscle adaptation with aging is complex. Recent work has revealed a novel role for small non-coding RNAs, called microRNAs (miRNA) in the regulation of gene expression. Using an integrated bioinformatics analysis of protein-coding gene and miRNA array data from young and older men, I identified ten specific miRNAs as important regulators of muscle plasticity (Plasticity Related miRs [PR-miRs]) leading to the transcriptional response to exercise and lean mass in young and older men. However, the precise mechanisms underlying the expression of PR-miRs on age-related changes in muscle anabolism and sarcopenia are currently unknown. Thus, the overall objective of this K01 application will be to determine the mechanistic role(s) of these PR-miRs in skeletal muscle adaptation to anabolic stimulation in 1) healthy young, 2) sarcopenic older and 3) age- and functionally-matched non-sarcopenic older males and females. This will be accomplished by determine the differences in expression of PR-miRs with aging and sarcopenia in response to anabolic stimulation (AIM 1). Mechanistically determine the extent to which manipulation of PR-miR levels in vitro, in human primary myocytes, can reverse anabolic resistance observed with age and sarcopenia (AIM 2) and the effect of altering PR-miRs levels on skeletal muscle growth and development (AIM 3). This project will improve our understanding of the molecular mechanisms that contribute to the loss of skeletal muscle and eventually leading to the development of drug therapies for the treatment of sarcopenia in the ever growing aging population. The mentorship team includes, Dr. Roger Fielding, a leader in aging research and muscle biology, Dr. Kenneth Walsh, a cardiovascular researcher and leading molecular biologist, Dr. Laurence Parnell a computational biologist and authority in gene and miRNA expression analysis, Dr. Thomas Gustafsson a physician-scientist and clinical researcher and Dr. Thomas Travison an expert in biostatistics. The mentorship team has a variety of know-how in every facet of this project including, conducting human clinical trials and skeletal muscle biology, computational biology and genomics and molecular biology and mechanisms. The proposed career development plan includes research-oriented and didactic training at Tufts University, Boston University and the Karolinska Institute in Stockholm, Sweden. The pursuit of the specific aims of the research project, the multidisciplinary mentorship team and the career development plan will facilitate a transition to an independent research career.